The present invention relates to a relay device that is mounted on a wiring board with solder and used for making and breaking contacts in a circuit and to a specific relay device mounting structure.
There is a relay device arranged on a power supply line for connecting a battery and an on-board load like a circuit in a vehicle relay box, for example, and used for switching contacts on the power supply line.
Such a relay device is formed such that terminals for making electrical connections to a circuit are drawn outside from a cover for containing a normally open (or closed) type switching contact member, a electromagnetic coil for causing the switching contact member to undergo excitation displacement toward the closed (or open) side and the like.
In the relay device thus constituted, the cover of the relay device is made of synthetic resin such as PBT (Polybutylene Terephthalate) and may undergo thermal expansion because of heat generation from the electromagnetic coil in case where the excitation toward the closed (or open) side of the contact continue for hours in duration.
When the thermal expansion occurs in the cover, there is generated external force of displacing the positions of the base end sides of the terminals drawn outside from the cover by a dimension corresponding to the quantity of the thermal expansion of the cover in a direction perpendicular to the extending direction of the terminals with respect to the positions of the front end sides joined to a wiring board with solder. Moreover, the external force acts on the base end portions of the terminals.
Heretofore, because packaging elements have been joined to wiring boards concerning relay boxes in conventional vehicles with solder using an eutectic (eutectic mixture) of Sb (tin) —Pb (lead), absorption of stress has been attempted without damaging the electrical connections between the terminals and the wiring boards by utilizing the absence of rigidity after hardening by cooling of the eutectic solder itself so as to make the solder absorb the stress countering the external force acting on the base end portions of the terminals at the time the cover thermally expands.
On the other hand, it is increasingly promoted to join packaging elements to wiring boards concerning relay boxes in vehicles of late years with solder made of material without containing Pb in view of the protection of the environment.
However, as solder made of material without containing Pb has extremely high rigidity after hardening by cooling, the adoption of a structure of making the solder absorb stress countering external force acting on the base end portions of terminals when the cover undergoes thermal expansion as before results in not allowing the solder affected by the stress to absorb the stress. Thus, the application of the stress is concentrated on the section between the solder and the wiring board and consequently the solder cake is peeled off the wiring board and alienated, so that the electrical connection between the terminal and the wiring board is damaged.
When terminals are joined to a wiring board with solder made of material without containing Pb in particular, it is needed to find a portion other than the solder in the soldering portion of each terminal with respect to the wiring board, that is, a portion where stress countering external force acting on the base end portion of the terminal at the time a cover undergoes thermal expansion without damaging the electrical connection between the terminal and the wiring board.
An object of the invention made in view of the situation above is to provide a relay device capable of absorbing stress countering external force produced in each terminal by the expansion and contraction of a cover due to heat generated by a heat generating element such as an electromagnetic coil without damaging the electrical connections between terminals and a wiring board, supposing that the front end portions of the respective terminals are joined to the wiring board with solder made of material without containing Pb.